1. Cross-Reference to Related Applications
This application is related to copending, commonly assigned Application No. 07/415,820 (Tucker), filed contemporaneously with this application, the disclosure of which is incorporated herein by reference.
2. Field of the Invention
This invention relates to electrical plugs, particularly electrical plugs which are useful for making an electrical connection between an electrical lead and an electrical power outlet.
2. Introduction to the Invention
It is known to insert a light, or other signal, into an electrical circuit so that it is easy to determine whether current is flowing through a heater or other operational electrical device which forms part of the circuit. The light can, for example, be placed in a plug through which the device is connected to a wall outlet in a building or to another power source. It is also known to insert a fuse, circuit breaker, ground fault circuit interrupter (GFCI), or other circuit protection device into an electrical circuit so that if the current exceeds a safe level or otherwise behaves in an abnormal fashion, the protection device is converted from its normal state into an abnormal state in which it disconnects the circuit from the power supply or otherwise prevents maintenance of the abnormal current. The protection device can, for example, be placed in a plug through which a heater or other operational device is connected to a wall outlet in a building or to another power source. When an electrical circuit contains both a signal light and a protection device, absence of the signal light may signify failure of the operational device itself, or failure of the electrical connections to the operational device, or conversion of the protective device into its abnormal state, e.g. failure ("blowing") of the fuse.
Self-regulating strip heaters which comprise elongate electrodes connected by a conductive polymer resistive element are well-known. In operation, the thermal output of these strip heaters varies in response to changes in the thermal environment and thus serves to limit the maximum temperature which the heater achieves. Such heaters are often used to provide freeze protection of pipes, such as domestic or commercial water lines, or to maintain a constant temperature for pipes in process industries. A number of measures have been proposed for assisting the safe operation of such heaters. Reference may be made, for example, to U.S. Pat. No. 4,436,986 (Carlson) and U.S. Pat. No. 4,822,983 (Bremner et al) and to copending commonly assigned application Ser. No. 404,730, filed Sept. 8, 1989 (Emmett). The disclosure of each of these patents and applications is incorporated herein by reference.